1. Field of the Invention
This invention relates to air cooling arrangements for electrical equipment and, more particularly, to an air cooling arrangement for electronic circuit cards wherein compressed air jets induce flow of ambient air for cooling.
2. Description of the Prior Art
Heat is produced whenever current flows, with only the possible exception of current flowing through a perfect conductor. Circuit and component miniaturization technologies are continuously reducing the amount of heat generated by each circuit component or subcircuit assembly, but packing density is increasing so fast that the heat generated per unit area on electronic circuit cards is not decreasing. With current high-performance logic circuits, a significant portion of the total equipment volume is devoted to fans or blowers, ducts, and other components associated with the cooling function.
A typical solution to the cooling problem is to force air through the equipment console. Hot spots still exist with this approach, which results in more sophisticated designs of interior layout or geometry of components and assemblies for optimum cooling. The generally accepted present approach to cooling is to provide multiple path airways through the equipment and to force air through the airways using at least one prime air mover such as a fan or blower. More sophisticated designs arrange the electronic assemblies such as circuit cards so as to channel or subdivide air flow in a predetermined desired manner. The cabinet itself is a part of many forced air cooling systems. As a result, opening a cabinet door and/or removing or repositioning a circuit card disturbs the conventional cooling system. Effective cooling may sometimes be lost to such an extent that thermally induced circuit failure may result if the electrical circuits are in operation. Even when circuit failure does not occur, the thermal environment of operating electrical components has been altered, which may alter circuit operation even though component failure does not occur. As a result, such servicing of equipment while it is "hot" (meaning in operation) is frequently difficult and sometimes impossible.
U.S. Pat. No. 3,626,251 teaches the use of high pressure air streams to direct or control a larger low pressure air stream toward hot spots. A blower is still the prime air mover, not the high pressure air streams, and the cooling system is still greatly disturbed when the servicing door is opened and to some extent also when a circuit board is removed or repositioned.